In order to produce high recording density on a hard disk and to improve the linear recording density, it is useful to increase the magnetic field gradient in the down-track direction (head scanning direction), thereby allowing the surface density produced by narrower tracks to be increased. The effects are that the down-track magnetic field gradient is increased by providing a trailing shield at the main magnetic pole, and the magnetic field leakage of the recording magnetic field to adjacent tracks is reduced by providing side shields. A wrap around shield (WAS) structure that has a trailing shield and side shields surrounding the main magnetic pole improves the signal-to-noise ratio (SNR) by increasing the down-track magnetic field gradient by using the trailing shield and reducing the effects on adjacent tracks by using the side shields.
The WAS structure described above is defined as a conformal WAS structure. The problems of conformal WAS structures are that the magnetic induction rate is effectively reduced and the magnetic field gradient does not increase when a magnetic wall is generated because the shape of the shield has many angles, as shown in FIG. 5, according to the prior art. The magnetization action of the shield is limited by this magnetic wall. The shield structure considered for solving this problem is the T-gap WAS structure shown in FIG. 6 in which the shield shape near the main magnetic pole places a gap (TS gap) between the trailing shield and the side shields. The magnetic wall is generated from a position separated from the main magnetic pole by this TS gap. The effective magnetic induction rate is improved by widening the region in which the magnetization tilts. Although the effects of using this T-gap WAS structure are an increased magnetic field gradient and a higher SNR, the problem of information erasure (ATI/FTI) in nearby tracks arises due to the difficulty in generating closure domains near the angle members at the trailing end of the side shields indicated by circles in FIG. 6, and the generation of the magnetic field leakage at locations where the magnetic load is concentrated.